The prior art discloses lighting devices for projection applications which comprise a phosphor arrangement having one or a plurality of phosphors. In this case, said lighting devices comprise a pump light source, which excites the phosphor to emit light having a different wavelength than the pump light wavelength (wavelength conversion of the pump light by means of phosphor). By means of suitable deflection of the pump light and the light emitted by the phosphor (conversion light), these two light beams can be brought together collinearly and fed to the imaging system.
Laser diodes are preferably used as the pump light source. In this case, the technology is also known by the designation LARP (“Laser Activated Remote Phosphor”). In order to distribute the laser power over a larger area on average over time and thus to reduce thermal quenching of the phosphor, inter alia, the at least one phosphor is usually applied to a wheel that rotates during operation. The lighting device thus emits light as a sequential succession of the spectrally different conversion light and, if appropriate, additionally the pump light, which, given a sufficiently rapid succession, are perceived as mixed light or, in combination with an imaging unit, as a color image.
Projectors are used for various applications that make different requirements of the technical lighting properties of the light from the light-generating unit. The spectral composition of this light determines the color rendering properties thereof and also the color space that can be represented therewith. For data projection, inter alia a bright white background is essential for text or graphical representations, compromises in the color rendering being acceptable. In home cinema applications, by contrast, the best possible color rendering with brilliant colors is sought. Therefore, specific projectors with phosphor wheels and filter wheels adapted to the envisaged (main) application are offered. In this case, the spectrum of the individual light colors of the projector (“color channels”) is determined and defined by the spectral properties of phosphor wheel and filter wheel rotating synchronously therewith. The luminous flux proportions of the color channels are defined by the segmentation of the different phosphors on the phosphor wheel and filter segments on the filter wheel. It is not possible to change the spectral properties of the projector during operation. Adaptation is generally possible only by exchanging the phosphor wheel and/or filter wheel. In this regard, projectors for home cinema applications require a larger red phosphor segment and/or additionally filtering in the direction of deep red. By contrast, larger green phosphor and yellow phosphor segments are customary for data projection.
The document CN 102385233 A discloses a lighting device for a projector comprising a pump laser, a phosphor wheel for the wavelength conversion of the pump laser light into conversion light, and a filter wheel, for spectrally filtering the conversion light. The pump laser light is directed onto the phosphor wheel with the aid of a dichroic mirror. The conversion light reflected back from the phosphor wheel passes through the dichroic mirror and impinges on the filter wheel. The pump laser light can pass through a transparency segment in the phosphor wheel and is fed to the dichroic mirror via a wraparound loop. The dichroic mirror reflects the pump laser light to the filter wheel. The filter wheel and the phosphor wheel are arranged on a common axis and thus rotate at the same speed.